chore(rds): RDS VersionUP follow-up in 2023.3 (#24426)

A day after the last commit, we got a bunch of updates! A bit frustrating:)

- [Amazon RDS for PostgreSQL now supports major version PostgreSQL 15](https://aws.amazon.com/about-aws/whats-new/2023/02/amazon-rds-postgresql-major-version-15/)
- [Amazon RDS for MariaDB supports new minor versions 10.6.12, 10.5.19, 10.4.28 and 10.3.38](https://aws.amazon.com/about-aws/whats-new/2023/02/amazon-rds-mariadb-new-minor-versions/)
- [Amazon Aurora MySQL 3.03 (compatible with MySQL 8.0.26) is generally available](https://aws.amazon.com/about-aws/whats-new/2023/03/amazon-aurora-mysql-3-03-compatible-mysql-8-0-26-available/)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-rds/lib/cluster-engine.ts

@@ -426,6 +426,8 @@ export class AuroraMysqlEngineVersion {
   public static readonly VER_3_02_1 = AuroraMysqlEngineVersion.builtIn_8_0('3.02.1');
   /** Version "8.0.mysql_aurora.3.02.2". */
   public static readonly VER_3_02_2 = AuroraMysqlEngineVersion.builtIn_8_0('3.02.2');
+  /** Version "8.0.mysql_aurora.3.03.0". */
+  public static readonly VER_3_03_0 = AuroraMysqlEngineVersion.builtIn_8_0('3.03.0');
 
   /**
    * Create a new AuroraMysqlEngineVersion with an arbitrary version.

packages/@aws-cdk/aws-rds/lib/instance-engine.ts

@@ -313,6 +313,8 @@ export class MariaDbEngineVersion {
   public static readonly VER_10_3_36 = MariaDbEngineVersion.of('10.3.36', '10.3');
   /** Version "10.3.37". */
   public static readonly VER_10_3_37 = MariaDbEngineVersion.of('10.3.37', '10.3');
+  /** Version "10.3.38". */
+  public static readonly VER_10_3_38 = MariaDbEngineVersion.of('10.3.38', '10.3');
 
   /** Version "10.4" (only a major version, without a specific minor version). */
   public static readonly VER_10_4 = MariaDbEngineVersion.of('10.4', '10.4');
@@ -334,6 +336,8 @@ export class MariaDbEngineVersion {
   public static readonly VER_10_4_26 = MariaDbEngineVersion.of('10.4.26', '10.4');
   /** Version "10.4.27". */
   public static readonly VER_10_4_27 = MariaDbEngineVersion.of('10.4.27', '10.4')
+  /** Version "10.4.28". */
+  public static readonly VER_10_4_28 = MariaDbEngineVersion.of('10.4.28', '10.4')
 
   /** Version "10.5" (only a major version, without a specific minor version). */
   public static readonly VER_10_5 = MariaDbEngineVersion.of('10.5', '10.5');
@@ -353,6 +357,8 @@ export class MariaDbEngineVersion {
   public static readonly VER_10_5_17 = MariaDbEngineVersion.of('10.5.17', '10.5');
   /** Version "10.5.18". */
   public static readonly VER_10_5_18 = MariaDbEngineVersion.of('10.5.18', '10.5');
+  /** Version "10.5.19". */
+  public static readonly VER_10_5_19 = MariaDbEngineVersion.of('10.5.19', '10.5');
 
   /** Version "10.6" (only a major version, without a specific minor version). */
   public static readonly VER_10_6 = MariaDbEngineVersion.of('10.6', '10.6');
@@ -366,6 +372,9 @@ export class MariaDbEngineVersion {
   public static readonly VER_10_6_10 = MariaDbEngineVersion.of('10.6.10', '10.6');
   /** Version "10.6.11". */
   public static readonly VER_10_6_11 = MariaDbEngineVersion.of('10.6.11', '10.6');
+  /** Version "10.6.12". */
+  public static readonly VER_10_6_12 = MariaDbEngineVersion.of('10.6.12', '10.6');
+
 
   /**
    * Create a new MariaDbEngineVersion with an arbitrary version.
@@ -1038,6 +1047,9 @@ export class PostgresEngineVersion {
   /** Version "14.6". */
   public static readonly VER_14_6 = PostgresEngineVersion.of('14.6', '14', { s3Import: true, s3Export: true });
 
+  /** Version "15" (only a major version, without a specific minor version). */
+  public static readonly VER_15 = PostgresEngineVersion.of('15', '15', { s3Import: true, s3Export: true });
+
   /**
    * Create a new PostgresEngineVersion with an arbitrary version.
    *
@@ -1335,7 +1347,6 @@ export class OracleEngineVersion {
   /** Version "19.0.0.0.ru-2023-01.rur-2023-01.r1". */
   public static readonly VER_19_0_0_0_2023_01_R1 = OracleEngineVersion.of('19.0.0.0.ru-2023-01.rur-2023-01.r1', '19');
 
-
   /** Version "21" (only a major version, without a specific minor version). */
   public static readonly VER_21 = OracleEngineVersion.of('21', '21');
   /** Version "21.0.0.0.ru-2022-01.rur-2022-01.r1". */